Sound programming is currently being distributed both for commercial and consumer applications in radio, television, cinematography and magnetic media. Prior art accomplish simultaneous transmission of digital text with analog sound in several ways: by means of providing a separate, independent digital sound channel in the same medium; by means of encoding digital data with the visual portion of analog television signals; by means of first digitizing the original analog sound and then by multiplexing or statistically coding additional digital data with said digitized sound sources; and, by means of first digitizing a portion of the original analog video signal and then by multiplexing or statistically coding additional digital text. Examples of such systems are described in U.S. Pat. No. 4,780,758.
A number of more specific prior art approach have been suggested and implemented, such as what is generically called Videotex, which is a digital text service employed in television that provides weather reports, news, stock market reports, theater and restaurant listings, advertisements, mailbox services, paging services and also allows access to various databases. In Videotex, the text is displayed either in color or in black-and-white on modified home TV receivers. "Teletext" is a subset of Videotex which describes variations of one-way-only services that connect information centers and their computers to provide electronic data files to users. At least one available line of the broadcast television vertical blanking interval (retrace) signal is used. "Videotex" is another subset of Videotex which refers to interactive systems typically using telephone lines or broadband coaxial cable distribution systems that are capable of sending data bi-directionally.
It has been discovered that: the statistical time-averaged sound spectrum of voice and musical instruments occupy only a small portion of its allocated bandwidth; human hearing has different thresholds of perceptibility for certain sound acoustical characteristics; the psychoacoustic character of sound such as pitch, loudness, timbre, duration, growth and decay, consonance, rhythm, presence and vibrato can be electrically manipulated without significantly altering the original sound's overall psychoacoustical character; human hearing is less sensitive to noise-like signals; high-frequency noise is masked by coherent sounds of definite pitch and higher levels; the dynamic characteristics of sound depend principally upon the loudness; the temporal characteristics involve time, duration, tempo and rhythm; the qualitative characteristics of sound involve timbre, or the harmonic constitution of the tone; a non-coherent, wideband, noise-like burst of data carrier signal is less likely to affect the overall tonal quality of the original sound; the tonal characteristics of sound involve pitch, timbre, melody, harmony, and all forms of pitch variants; the upper limit of pitch, a sensory characteristic arising out of the frequency assigned to a tone, as perceived by an average individual under forty years of age, with good hearing, unimpaired by disease or injury is around 15 KHz; in another psychoacoustic characteristic called pitch discrimination, which is one's ability to differentiate the pitch between two sounding tones, one can not discriminate the presence of a 15 KHz tone that is sounded simultaneously with another tone of lower frequency and lower in level by at least ten decibels; and, another psychoacoustic characteristic called Duration of Sound which is related to pitch discrimination indicates that a tone of certain amplitude in the presence of another tone with a different amplitude must persist for a certain length of time in order to detect a change in pitch--if the duration of the tone is very short, then it appears as a click--if somewhat longer, then it appears as noise with some attribute of pitch--as the length of sounding time is increased, it finally becomes a tone of definite pitch--at high frequencies, it takes greater than 1 milliSeconds to ascribe a definite pitch.
The fundamental problems with the prior art approach in Radio, Television, Cinematography and magnetic media for text transmission are: the unavailability of additional sound channels, the inflexibility of broadcast frequency assignments; inefficient methods of modulation; and, the limited number of frequencies that are applicable in the existing equipment infrastructure. Additionally, prior art encoding and decoding methods are complex, expensive, and often require extensive modifications or a complete replacement of existing equipment. For the said reasons, there exists a need for new methods of telecommunications, particularly for transmission of digital text over analog sound that is capable of operating compatibly with existing apparatus for both commercial and consumer use.
The present invention eliminates the problems and disadvantages of prior art approaches.